Various functionalities such as waterproofness and cold protection in addition to soft texture are required for fiber products such as clothes depending on the purpose of use. For example, excellent waterproofness is required for sports wears such as mountaineering wears for the purpose of preventing penetration of rainwater or the like, and in the case of jobs requiring wearing of specific uniforms as in policemen and firemen, properties such as cold protection and thermal insulation are required for the uniforms and the like in some cases. Further, barrier properties for preventing soil of beds and futons due to excretion such as urine in addition to good touch feeling and prevention of stuffiness are required for sheets used for hospital beds and the like in some cases.
As fiber products such as clothes and sheets provided with such properties, for example, a multilayer sheet, which is obtained by selecting a plurality of fibrous substrates or resin films depending on the required properties and stacking them is known.
As the above multilayer sheet, there is known, for example, a wear for cold protection and thermal insulation including an adhered laminate of raised fabric or pile fabric and a permeable polymer film, wherein the permeable polymer film is stacked on and adhered onto the raised surface or pile surface of the fabric with a curing reaction type-adhesive interposed therebetween, the weight of the wear is 50 g to 400 g per m2 and the amount of the adhesive applied is 2 g to 30 g per m2, and the permeable polymer film surface is positioned on the front surface side of the wear (see, for example, Japanese Patent Laying-Open No. 2002-327310).
Further, as the curing reaction-type adhesive usable for production of the above wear for cold protection and thermal insulation, it is known that a moisture-curable hot melt adhesive containing a urethane prepolymer can be used, and it is also known that the above polymer film and the above fabric are adhered by the curing reaction-type adhesive applied in a dot pattern, and thereby a wear having a good heat retaining property without impairing soft texture required for a wear can be obtained.
However, a multilayer sheet obtained using the above conventional moisture-curable polyurethane hot melt adhesive sometimes caused reduction in adhesion strength of the adhesive by repeated water washing or dry cleaning, thereby causing separation between substrates constituting the multilayer sheet.
Therefore, the development of an adhesive which can exhibit excellent adhesion strength for various substrates and hardly causes separation between substrates even when water washing or dry cleaning is repeatedly performed has been progressed. As such an adhesive, there is known, for example, a reactive hot melt adhesive obtained by reacting a polyisocyanate (A) with a polyol (B), wherein the polyol (B) contains a polyolefin polyol (C), a xylene resin (D), rosins (E), a polyester polyol (F) and a polyether polyol (G) as essential components (see, for example, Japanese Patent Laying-Open No. 2005-290280).
Meanwhile, cleanliness at an extremely high level and excellent sanitary conditions are required for sheets used for beds and futons of a hospital, and therefore the sheets are separately handled from general household washes in many cases. As the washing method, there is known a method in which general water washing is performed, and then high temperature washing is performed at generally 50 to 90° C. using a detergent, an alkaline agent, a bleach and the like, and sterilization and disinfection treatment is successively performed under pressure at high temperature. Such a washing method generally referred to as “industrial washing” significantly reduces adhesion strength of an adhesive used for production of a multilayer sheet in some cases due to a large load applied to a multilayer sheet such as sheets as compared with usual water washing, dry cleaning or the like.
Here, in the case of a multilayer sheet produced using the above reactive hot melt adhesive, separation between substrates could be prevented to some extent even when water washing or dry cleaning was repeatedly performed. However, when the multilayer sheet was repeatedly subjected to industrial washing, the adhesion strength of the reactive hot melt adhesive was significantly reduced and thereby separation between substrates was caused in some cases.
As described above, there has not yet been found under the present circumstances an adhesive which can exhibit such a level of adhesion strength that the separation between substrates constituting a multilayer sheet is not caused and does not impair soft texture of clothes and the like even when washing is repeatedly performed under stringent washing conditions.